Postage meters are mass produced devices for printing a defined unit value for governmental or private carrier delivery of parcels and envelopes. The term postage meter also includes other like devices which provide unit value printing such as tax stamp meters. Postage meters include internal accounting devices which account for postage value representation which is stored within the meter and is printed by the meter. As the result, postage meters must possess an extremely high reliability to avoid the loss of user or government funds stored within the meter.
Electronic postage meters have been developed with electronic accounting circuitry. Postage meter systems of this type are disclosed in U.S. Pat. No. 3,978,457 for MICROCOMPUTERIZED ELECTRONIC POSTAGE METER SYSTEM; in U.S. Pat. No. 4,301,507 for ELECTRONIC POSTAGE METER HAVING PLURAL COMPUTING SYSTEMS; and, in U.S. Pat. No. 4,559,443 for INITIALIZING THE PRINT WHEELS IN AN ELECTRONIC POSTAGE METER. The electronic accounting circuits of the meter include non-volatile memory capability for storing postage accounting information. The memory function in the electronic accounting circuits have replaced the function served in mechanical postage meters by mechanical accounting registers. The non-volatile memory and value selection in the electronic postage meters of the aforementioned patents as well as other meter functions are operated under microcomputer control.
Postage meters with mechanical accounting registers are not subject to many of the problems encountered by electronic postage meters. Conditions cannot normally occur in postage meters with mechanical registers that prevent, for example, accounting for a printing cycle or which result in the loss of data stored in the mechanical registers. This is not the case with electronic postage meters. Electronic components are subject to the effects of electromagnetic radiation which can affect their operation. Thus, precautions must be taken as for example by proper shielding to protect the meter's electrical components from the effects of electromagnetic radiation. Mechanical security must, of course, also be provided. Moreover, in electronic postage meters, the reliability of the meter is dependent, in part, on the reliability of the electronic components including the microcomputer with its related circuitry and the meter non-volatile memory. Accordingly, it has been noted that it is desirable to have high reliability in electronic postage meters.